text: The reagent for the K test is an aqueous solution of potassium hydroxide (KOH) (10–25%), or, in the absence of KOH, a 10% aqueous solution of sodium hydroxide (NaOH, lye), which provides nearly identical results. A 10% solution of KOH will retain its effectiveness for about 6 months to a year. The test depends on salt formation and requires the presence of at least one acidic functional group in the molecule. Lichen compounds that contain a quinone as part of their structure will produce a dark red to violet colour. Example compounds include the pigments that are anthraquinones, naphthoquinones, and terphenylquinones. Yellow to red colours are produced with the K test and some depsides (including atranorin and thamnolic acid), and many β-orcinol depsidones. In contrast, xanthones, pulvinic acid derivatives, and usnic acid do not have any reaction.
  Some common and widely distributed lichens that have lichen products with a positive reaction to K include Xanthoria parietina, which is K+ (red-purple) due to the parietin (an anthraquinone), and Dibaeis baeomyces, which is K+ (yellow), due to the didepside compound baeomycesic acid.